Investigation of the physiological basis for increased exercise threshold for angina pectoris after physical conditioning.

Eight patients with coronary heart disease and exertional angina pectoris successfully completed an 11-15 wk program of endurance exercise conditioning. Angina threshold was determined by upright bicycle ergometer exercise and by atrial pacing. The product of heart rate and arterial systolic blood pressure at the exercise angina threshold was higher after conditioning. suggesting that conditioning increased the maximum myocardial O(2) supply during exercise. However, when angina was induced by atrial pacing, heart rate, arterial blood pressure, coronary blood flow, and myocardial O(2) consumption at the angina threshold were the same before and after conditioning. Myocardial lactate extraction during atrial pacing was abnormal in the same five patients before and after conditioning. Conditioning caused no detectable changes in coronary collaterals as judged by coronary arteriograms. The increase in exercise angina threshold appeared to be due to a functional adaptation in either myocardial O(2) supply or the relationship between hemodynamic work and myocardial O(2) consumption. The adaptation was limited to exercise, and did not occur during a different stress to myocardial O(2) supply, atrial pacing.